[PATCH RFC v3 02/10] usb: misc: qcom_eud: add sysfs attribute for port selection

[Elson Serrao <elson.serrao@oss.qualcomm.com>]

EUD can be mapped to either the primary USB port or the secondary USB port
depending on the value of the EUD_PORT_SEL register. Add a 'port' sysfs
attribute to allow userspace to select which port EUD should operate on
and update the ABI documentation. This is needed for systems with dual
USB ports where EUD needs to be accessible on either port depending on the
system configuration and use case.

Signed-off-by: Elson Serrao <elson.serrao@oss.qualcomm.com>
---
 Documentation/ABI/testing/sysfs-driver-eud | 16 ++++++++
 drivers/usb/misc/qcom_eud.c                | 43 ++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-eud b/Documentation/ABI/testing/sysfs-driver-eud
index 2bab0db2d2f0..67223f73ee60 100644
--- a/Documentation/ABI/testing/sysfs-driver-eud
+++ b/Documentation/ABI/testing/sysfs-driver-eud
@@ -7,3 +7,19 @@ Description:
 		EUD based on a 1 or a 0 value. By enabling EUD,
 		the user is able to activate the mini-usb hub of
 		EUD for debug and trace capabilities.
+
+What:		/sys/bus/platform/drivers/qcom_eud/.../port
+Date:		January 2026
+Contact:	Elson Serrao <elson.serrao@oss.qualcomm.com>
+Description:
+		Selects which USB port the Embedded USB Debugger (EUD)
+		is mapped to on platforms providing multiple High-Speed
+		USB ports.
+
+		Valid values:
+		  0 - Primary USB port
+		  1 - Secondary USB port
+
+		The attribute is writable only while EUD is disabled.
+		Reading the attribute returns the currently selected
+		USB port number.
diff --git a/drivers/usb/misc/qcom_eud.c b/drivers/usb/misc/qcom_eud.c
index 926419ca560f..1a136f8f1ae5 100644
--- a/drivers/usb/misc/qcom_eud.c
+++ b/drivers/usb/misc/qcom_eud.c
@@ -23,8 +23,11 @@
 #define EUD_REG_VBUS_INT_CLR	0x0080
 #define EUD_REG_CSR_EUD_EN	0x1014
 #define EUD_REG_SW_ATTACH_DET	0x1018
+#define EUD_REG_PORT_SEL	0x1028
 #define EUD_REG_EUD_EN2		0x0000
 
+#define EUD_MAX_PORTS		2
+
 #define EUD_ENABLE		BIT(0)
 #define EUD_INT_PET_EUD		BIT(0)
 #define EUD_INT_VBUS		BIT(2)
@@ -40,6 +43,7 @@ struct eud_chip {
 	int				irq;
 	bool				enabled;
 	bool				usb_attached;
+	u8				port_idx;
 };
 
 static int enable_eud(struct eud_chip *priv)
@@ -104,8 +108,47 @@ static ssize_t enable_store(struct device *dev,
 
 static DEVICE_ATTR_RW(enable);
 
+static ssize_t port_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct eud_chip *chip = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%u\n", chip->port_idx);
+}
+
+static ssize_t port_store(struct device *dev,
+		struct device_attribute *attr,
+		const char *buf, size_t count)
+{
+	struct eud_chip *chip = dev_get_drvdata(dev);
+	u8 port;
+	int ret;
+
+	ret = kstrtou8(buf, 0, &port);
+	if (ret)
+		return ret;
+
+	/* Only port 0 and port 1 are valid */
+	if (port >= EUD_MAX_PORTS)
+		return -EINVAL;
+
+	/* Port selection must be done before enabling EUD */
+	if (chip->enabled) {
+		dev_err(chip->dev, "Cannot change port while EUD is enabled\n");
+		return -EBUSY;
+	}
+
+	writel(port, chip->base + EUD_REG_PORT_SEL);
+	chip->port_idx = port;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(port);
+
 static struct attribute *eud_attrs[] = {
 	&dev_attr_enable.attr,
+	&dev_attr_port.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(eud);
-- 
2.34.1